Definition of basal metabolism in mammals and man

Blaxter 1962 [1] p. 79 f: "It has long been realized that if an animal is given no food and certain other conditions are met, a measurement of heat production represents that animal's minimal energy demand. Measurments of this type are called basal metabolism determinations, and the conditions for the measurement are, firstly, that the animal should be in a post-absorptive state, secondly, that it should be in a state of muscular repose though not asleep and, lastly, that the environment in which the measurement is made should be neither so hot nor so cold as to cause and increase in the metabolism. This last condition means that the animal should be in a 'thermoneutral' environment." .. "In man, basal metabolism is measured with the subject in repose but not asleep. Sleep during fasting depresses metabolism by about 7%." .. "With man, an overnight fast is sufficient to achieve a post-absorptive state and to reduce metabolism to a basal level. Indeed it is even permissible for clinical purposes to take a very slight ultra-continental breakfast before the measurement is made, since it has little effect on the metabolism determined a few hours later."

States and rates

Respiratory states: from physiology to cellular and mitochondrial respiration

Routine respiration is usually higher than standard or basal respiration due to the oxygen consumption required to sustain various routine activities, not restricted to locomotory activity, but including the effects of food or substrate availability, growth conditions. In intact cells, ROUTINE respiration varies as a function of cell cycle and substrate supply ([5,6]).

Resting respiration in cells and mitochondrial preparations may refer to the LEAK state of minimum respiration (inhibition of phosphorylation, e.g. by oligomycin or deprivation of ADP]. If 'basal' is taken as 'minimum' (e.g. basal body temperature is the lowest body temperature attained during rest), then basal respiration in cells and mitochondria is the minimum respiration in the LEAK state [7,8]. A recently proposed terminology uses the term 'basal respiration' to describe ROUTINE respiration of intact cells, which proceeds at an intermediate rather than minimum ATP demand [9]. This definition lacks physiological context, is confusing, and its use is discouraged [8].

LEAK respiration is the energy expenditure required mainly to compensate for the proton leak through the inner mitochondrial membrane, but additionally including energy expenditure caused by proton slip and cation cycling through the inner mitochondrial membrane in general [7,8]. LEAK or basal respiration in mitochondrial preparations is obtained after inhibition of phosphorylation or in the absence of ADP in ET-pathway competent substrate states [7]. LEAK or basal respiration is measured in intact cells after inhibition of phosphorylation (e.g. oligomycin) and should be corrected for residual oxygen consumption (ROX [5]).

Metabolic energy flow, flux, and rate

The term metabolic 'rate' is frequently used for energy flow or metabolic flux. Energy flow (oxygen flow) is system-specific quantity related to a defined system, and expressed per system (per individual organism, per million cells, or per experimental system). Metabolic flux (oxygen flux) is a system size-specific quantity, expressed per kg body weight, per volume, or per surface area of the body [10].